ES2917474T3 - Apparatus for manufacturing three-dimensional objects by continuous and discontinuous solidification - Google Patents

Abstract

A method and apparatus for making a three-dimensional object by solidifying a solidifiable material are shown and described. A photopartition inhibitor is admitted to one surface of a photographic frame material to create a "dead zone" where little or no solidification occurs. The dead zone prevents the exposed surface of the photowrapping material from solidifying in contact with a bottom or container film. As the solidified object areas get larger and the speed of the build platform increases, the dead zone increases, which can cause channeling in the objects and resulting delamination. A number of techniques are disclosed including continuous/discontinuous mode switching, multiple illuminations of portions of the same layer, and the use of gray scale to regulate the size of the dead zone. (Automatic translation with Google Translate, without legal value)

Description

DESCRIPTION

Apparatus for manufacturing three-dimensional objects by continuous and discontinuous solidification

Countryside

The disclosure relates to a system and method for manufacturing three-dimensional objects and, more specifically, to a system and method in which movement of a build platform and exposures to solidification energy are carried out continuously and discontinuously in Different moments.

Description of Related Art

Rapid 3D prototyping and manufacturing enable fast and precise production of components with high precision. Machining steps may be reduced or eliminated by such techniques and certain components may be functionally equivalent to their regular production counterparts depending on the materials used for production.

The components produced can range in size from small to large parts. Part manufacturing can be based on a variety of technologies, including photopolymer hardening using light or laser curing procedures. Secondary curing can take place with exposure to, for example, ultraviolet (UV) light. A process for converting computer-aided design (CAD) data into a data model suitable for rapid manufacturing can be used to produce data suitable for building the component. A pattern generator can then be used to build the part. An example of a pattern generator may include the use of Texas Instruments® DLP (Digital Light Processing technology), SXRD™ (X-tal Silicon Reflective Display), LCD (Liquid Crystal Display), LCOS (Liquid Crystal in silicon), DMD (Digital Mirror Device), JVC's J ILA, SLM (Spatial Light Modulator) or any kind of selective light modulation system.

In certain manufacturing processes for three-dimensional objects, it is important to ensure that the settable material (eg, polymeric resin) used to make the object forms a smooth, substantially flat surface to which the setting energy of a pattern generator will be applied. One technique uses an "upside down" build process in which an object is built progressively in the direction of the downward (z) build axis (toward the ground) as the build platform is progressively raised in the direction of the downward (z) axis. ascending construction (z). A trough containing the solidifiable material, such as a photoresist material, has a transparent bottom through which solidification energy patterns are projected to solidify the photoresist material in patterns corresponding to cross-sections of the three-dimensional object. However, because the solidification energy is incident on the bottom of the cuvette, the photoresist material solidifies on contact with the cuvette and must be removed without damaging the object.

Certain known procedures involve creating a "dead zone" (where no solidification occurs) in a thin region at the interface between the photoresist material and the bottom of the cuvette. These procedures avoid the need for a means to separate the solidified object from the bottom of the bucket. The procedures typically involve feeding a photoresist inhibitor into the thin region. Typically, the inhibitor reacts with or consumes a polymerization initiator such that polymerization cannot occur within the thin region. The inhibitor is fed at a rate that affects the thickness of the dead zone. Because no separation step is required, some of the methods move the build platform continuously up along the build axis to speed up the build process. However, for objects that have certain cross-sectional areas, the speed at which the build platform can be raised is limited by the speed at which the solidifiable material fills the space left by the solidified material used to build it. form the most recent layer. As the settable material flows faster into the gap, a pressure drop between the inhibitor and the periphery of the partially formed object increases, causing the flow rate of the inhibitor at the periphery to increase. This, in turn, increases the thickness of the construction axis (z) of the dead zone. Expansion of the dead zone in this way can cause channels to form in the part and eventually delamination of the object. Therefore, a need has arisen for a system and method for fabricating three-dimensional objects that addresses the above issues.

WO 2015/195924 A1 discloses an apparatus according to the preamble of claim 1.

Brief description of the drawings

The disclosure will now be described, by way of example, with reference to the accompanying drawings, in which:

Fig. 1A is a cross-sectional side elevational view of the system for fabricating a three-dimensional object from a settable material in accordance with the present disclosure;

Fig. 1B is a close-up, side elevation, and cross-sectional view of a build platform and photoresist container in a first configuration prior to solidification of a layer of photoresist material;

Fig. 1C is a close-up, side elevation, and cross-sectional view of a build platform and photoresist container in a second configuration after solidification of a layer of photoresist material;

Fig. 2 is a close-up cross-sectional view of a first example of a photoresist tray for use in the system of Fig. 1A;

Fig. 3 is a close-up cross-sectional view of a second example of a photoresist tray for use in the system of Fig. 1A;

Fig. 4 is a close-up cross-sectional view of a third example of a photoresist tray for use in the system of Fig. 1A;

Fig. 5 is a flow chart depicting a method of operating the system of Fig. 1A, in which an object construction process includes both continuous and batch modes of operation;

Fig. 6 is a graph depicting a method, not forming part of the present invention, for operating the system of Fig. 1A, in which different exposure times are used for different independent continuous regions of a layer of a three-dimensional object;

Fig. 7 is a graph depicting a series of bitmaps corresponding to the exposure times of Fig. 6;

Fig. 8 is a graphical representation of object data for four independent continuous regions of a three-dimensional object layer;

Fig. 9 is a bitmap used to form the four independent continuous regions of an object layer shown in Fig. 8;

Fig. 10 is a flow diagram depicting a method, not part of the present invention, for fabricating a three-dimensional object using the exposure time profile of Fig. 6 and the bitmaps of Fig. 7 ;

Fig. 11 is a flowchart showing a method, not forming part of the present invention, for manufacturing a three-dimensional object using the bitmap of Fig. 9;

Fig. 12 is a bitmap of an independent continuous region of an object with internal void areas used to demonstrate the calculation of the ratio of an internal void area to an external boundary area ("void ratio" );

Fig. 13 is a table used to illustrate a method, not forming part of the present invention, for determining a dead time used in a method for manufacturing a three-dimensional object; Fig. 14A is a representation of a first independent continuous region defined by object data for a layer of a three-dimensional object used to illustrate a method for determining the longest minimum path of the region and layer;

Fig. 14B is a representation of a second independent continuous region defined by object data for the object layer of Fig. 14A used to illustrate a method for determining the longest minimum path of the second continuous region;

Fig. 15A is a table used to illustrate a method, not forming part of the present invention, for determining a build platform speed in a method for manufacturing a three-dimensional object; Y

Figs. 15B-15D are tables used to illustrate a method, not part of the present invention, for determining grayscale value contributions to total grayscale values for maintaining a dead zone height in a manufacturing process. of a three-dimensional object.

Detailed description

The figures illustrate examples of a manufacturing system and method. Based on the foregoing, it should be generally understood that the nomenclature used herein is for convenience only and the terms used to describe the invention should have the broadest meaning to one skilled in the art.

The system and methods described herein are generally applicable to the additive manufacturing of three-dimensional objects, such as components or parts (discussed generally herein as objects), but may be used beyond this scope in alternative applications. The system and methods generally involve creating a non-solidification "dead zone" in a photoresist material to prevent the material from solidifying against a surface of a photoresist container. Various techniques are described below to avoid excessive expansion of the dead zone along the construction (z) axis. In one method, sets of continuous and discontinuous solidification energy image exposure periods alternate. In another method, not part of the present invention, selected portions of an object layer are exposed to solidification energy multiple times to achieve the required layer thickness. In another method, not part of the present invention, the solidification energy intensity is varied between selected areas of an object to achieve the required layer thickness.

According to a first aspect of the present disclosure, which is not part of the present invention, there is provided a method of fabricating a three-dimensional object by imaging solidification energy onto a photoresist material that solidifies on a build platform. . The method comprises admitting a photoresist inhibitor through a surface of the photoresist material, continuously moving the build platform along a build axis away from the surface during each period in a first set of consecutive periods, and moving discontinuously the build platform along the build axis away from the surface for a second set of consecutive periods. During the first set of consecutive periods, an uninterrupted series of image exposures is sequentially made on the surface, where each image is representative of a corresponding cross-section of the three-dimensional object. During the second set of consecutive periods, a series of image exposures are made sequentially on the surface, with the build platform not moving during any of the image exposures and moving away from the surface when no image exposures occur. . In certain examples, the continuous motion and discontinuous motion steps are performed in an alternating sequence. In certain examples, the procedure is carried out when an individual area with the largest cross section of the three-dimensional object exceeds a selected value. In other examples, the frequency of alternation between continuous and discontinuous motion depends on the value of the single area with the largest cross section of the three-dimensional object. In other examples, the number of consecutive exposure periods in the first set and the second set may be the same or different.

In accordance with another aspect of the present disclosure, a method of fabricating a three-dimensional object by projecting solidification energy onto a photoresist material that solidifies on a build platform is provided. The method comprises alternating between sets of continuous freezing energy image exposure periods and sets of discontinuous freezing energy exposure periods. During each set of continuous solidification energy image exposure periods, solidification energy images corresponding to cross-sections of the three-dimensional object are continuously projected onto a surface of the photoresist material as the build platform moves continuously. continues a distance along a build axis corresponding to a selected number of object layers, and during each set of discontinuous solidification energy exposure periods, the build platform moves discontinuously along the axis and solidification energy images corresponding to cross-sections of the three-dimensional object are discontinuously projected onto the surface of the photoresist material to solidify the selected number of layers only when the build platform is stationary along the axis of building. In certain examples, the procedure is carried out when an individual area with the largest cross section of the three-dimensional object exceeds a selected value. In other examples, the frequency of alternation between continuous and discontinuous sets of solidification energy exposure periods depends on the value of the single largest cross-sectional area of the three-dimensional object.

In accordance with yet another aspect of the present disclosure, which is not part of the present invention, a method of manufacturing a three-dimensional object by solidifying a solidifiable material on a build platform is provided. The method comprises providing a first object data set that defines a layer of the three-dimensional object, providing a second object data set that is a subset of the first object data set, supplying a first solidification energy pattern corresponding to the first object data set for a first exposure time to a build region in the solidifiable material as the build platform moves along a build axis, where the first solidification energy pattern passes through a zone dead in the solidifiable material in which no solidification takes place. The method also comprises supplying a second solidification energy pattern corresponding to the second set of object data for a second exposure time to the build region, where the second solidification energy pattern passes through the dead zone.

In accordance with yet another aspect of the present disclosure, which is not part of the present invention, a method of manufacturing a three-dimensional object by solidifying a solidifiable material is provided. The method comprises providing sets of object data, where each set corresponds to a layer of the object, solidifying a plurality of layers of the solidifiable material according to a corresponding set of the object data to form the three-dimensional object on a build platform, wherein the build platform moves continuously along the build axis during the solidification step of each of the plurality of layers, and wherein during the solidification of each of the plurality of layers, at a first set of independent continuous regions of the layer, meeting a first specified surface area criterion, a first specified slenderness criterion, and a first specified internal void area to external boundary area ratio criterion, is supplied with power from solidification corresponding to a first grayscale value, and to a second set of regions co Independent continuous lines, meeting a second specified surface area criterion, a second specified slenderness criterion, and a second specified internal void area to external boundary area ratio criterion, are supplied with solidification energy corresponding to a second value of grayscale.

According to a further aspect of the present disclosure, which is not part of the present invention, there is provided a method of manufacturing a three-dimensional object by solidifying a solidifiable material comprising providing object data for a plurality of layers of the three-dimensional object , where the object data for each layer define one or more independent continuous regions of the object, select a desired layer thickness for each layer, determine a maximum longest minimum path for each independent continuous region in each layer, determine a longest minimum path longest minimum path ("LMP") for each independent continuous region in the layer, determine a dead time for each layer based on the maximum longest minimum path for each layer, and determine at least one exposure time for each layer, each exposure time corresponding to one or more continuous regions of the layer. The method further comprises solidifying each layer of the plurality of layers of the solidifiable material to form a corresponding layer of the plurality of layers of the three-dimensional object by moving a build platform along a build axis during the layer dead time, where no solidification of the solidifiable material occurs during the dead time, continuing to move the build platform along the build axis while projecting a sequence of solidification energy patterns onto the solidifiable material, each pattern corresponding to one of at least an exposure time, where the sequence progresses from a first pattern corresponding to all independent continuous regions to a last pattern corresponding to one of the one or more independent continuous regions having the longest minimum path greater than the others of the one or more more independent continuous regions.

The system is generally used to fabricate three-dimensional objects from a solidifiable material and rapid prototyping. A pattern generator (such as a digital light projector, laser, LCD, LED array, etc.) provides an image to the settable material to selectively set it.

As discussed herein, a settable material is a material that, when subjected to energy, fully or partially hardens. This reaction to solidification or partial solidification can be used as the basis for building the three-dimensional object. Examples of a curable material may include a polymerizable or crosslinkable material, a photopolymer, photopowder, photopaste, or a photosensitive compound containing any type of ceramic-based powder, such as aluminum oxide or zirconium oxide or itera-stabilized zirconium oxide, a curable silicone composition, siliceous-based nanoparticles or nanocomposites. The settable material may further include fillers. Furthermore, the settable material may take a final form (eg, after exposure to electromagnetic radiation) which may vary from semi-solids, solids, waxes, and crystalline solids. A photocurable material is a material that, when subjected to electromagnetic energy of a particular intensity and for a particular period, hardens by polymerization and/or crosslinking (curing).

When speaking of a photopolymerizable, photocurable or solidifiable material, it is meant any material, possibly comprising a resin and optionally additional components, which can be solidified by supplying stimulating energy, such as electromagnetic radiation. Suitably, a material that is polymerizable and/or crosslinkable (ie curable) by electromagnetic radiation (currently most common wavelengths include UV radiation and/or visible light) can be used as said material. In one example, a material comprising a resin formed from at least one ethylenically unsaturated compound (including, but not limited to, (meth)acrylate monomers and polymers) and/or at least one compound containing an epoxy group. Other suitable components of the settable material include, for example, inorganic and/or organic fillers, coloring substances, viscosity controlling agents, etc., but are not limited thereto.

When photopolymers are used as the settable material, a photoinitiator is typically provided. The photoinitiator absorbs light and generates free radicals that initiate the polymerization and/or crosslinking process. Suitable types of photoinitiators include metallocenes, 1,2-di-ketones, acylphosphine oxides, benzyldimethyl ketals, α-amino ketones, and α-hydroxy ketones. Examples of suitable metallocenes include Bis(eta 5-2,4-cyclopenadien-1-yl) Bis[2,6-difluoro-3-(1H-pyrrol-1-yl)phenyl]titanium, such as Irgacure 784, available from Ciba Specialty Chemicals. Examples of suitable 1,2 di-ketones include quinones such as camphorquinone. Examples of suitable acylphosphine oxides include bis-acylphosphine oxide (BAPO), which is available under the name Irgacure 819, and monoacylphosphine oxide (MAPO), which is available under the name Darocur® TPO. Both Irgacure 819 and Darocur® TPO are supplied by Ciba Specialty Chemicals. Examples of suitable benzyldimethyl ketals include alpha,alphadimethoxy-alpha-phenylacetophenone, which is available under the name Irgacure 651. Suitable a-amino ketones include 2-benzyl-2-(dimethylamino)-1-[4-(4-morpholinyl) phenyl]-1-butanone, available under the name Irgacure 369. Suitable a-hydroxy ketones include 1-hydroxy-cyclohexyl-phenyl-ketone, available under the name Irgacure 184 and a 50-50 mixture (by weight) of 1-hydroxy-cyclohexyl-phenyl-ketone and benzophenone, which is supplied under the name Irgacure 500.

The pattern generator(s) can be configured in various ways. Many can provide controlled electromagnetic radiation to provide a desired pattern. Electromagnetic radiation may include actinic light, visible or invisible light, UV radiation, IR radiation, electron beam radiation, X-ray radiation, laser radiation, or the like. Furthermore, while each type of electromagnetic radiation in the electromagnetic spectrum can be discussed in general terms, the disclosure is not limited to the specific examples provided. Those skilled in the art are aware that variations in the type of electromagnetic radiation and methods for generating the electromagnetic radiation can be determined based on the needs of the application.

Referring to Fig. 1A, a system 20 is shown for fabricating a three-dimensional object 24 from a photoresist material 25. The system 20 is generally configured to receive data describing the shape and appearance of the object (such as CAD data) and to create a solid object 24 in accordance with the data. System 20 includes a housing 22 in which a pattern generator 37 is disposed. Pattern generator 37 projects two-dimensional solidification energy images upward along a build axis (z) and through an opening 34 in the top of the housing 22. The photocurable material 25 is a material that, when subjected to electromagnetic energy of a particular intensity and for a particular period, hardens by polymerization and/or crosslinking (curing). Each image projected by pattern generator 37 corresponds to a cross-section of three-dimensional object 24. Photohardenable material 25 is contained in a container 28 with a transparent bottom. Container 28 is positioned over an opening 34 in the top of housing 22 so that electromagnetic energy (such as UV, IR, or visible light) can enter container 28. At least one process computer is operatively connected to the container. pattern generator 37 and a build platform actuator (not shown) to provide image data to the pattern generator 37 for moving the build platform 26 along the build axis (z). One of the process computers or another computer may be provided to convert image data from one format (eg .stl files) to another suitable for use by the pattern generator (eg bitmaps).

Solidification of the photoresist material 25 occurs in a build region beginning at a build plane 32. The build plane 32 is defined by a dead zone 41 (Figs. 2-4), which is a region into which it penetrates solidification energy but in which the photoresist material 25 does not harden. In certain examples, the dead zone 41 is created by feeding a photoresist inhibitor 47 into the container 28 or a portion thereof containing the photoresist material 25. In the same or other cases, the temperature of the dead zone 41 is controls to inhibit polymerization.

Container 28 can be structured in a number of different ways. An exemplary configuration is shown in Fig. 2. Container 28 includes a transparent bottom 36 comprised of a rigid or semi-rigid material, such as glass or plastic. An inhibitor-permeable film 33 defines a transparent surface that is permeable to photohardening inhibitor and is spaced from the bottom 36 along the build axis (z). Photocurable material 25 is over and in contact with inhibitor permeable film 33. Inhibitor permeable film 33 is attached to the sides of frame 38 defining the side walls of container 28. Film 33 sits on a central flange 49 defining a central opening 48. Flange 49 projects upwardly from shelf 42. A chamber 46 is defined between film 33 and transparent bottom 36. Chamber 46 acts as a reservoir for photohardening inhibitor 47 and has a internal pressure that can be regulated by the flow of inhibitor 47 in the vessel and/or the speed of movement of the build platform 26 away from the build plane 32. Inhibitor inlets 39a and 39b are connected to a source of inhibitor 47. Preferably, inhibitor 47 is selected to be reactive with and consume a polymerization initiator in photoresist material 25. Exemplary inhibitors 47 include oxygen and air. Inhibitor enters chamber 46 through inlets 39a and 39b and permeates inhibitor-permeable film 33 through central opening 48 to contact exposed (lower) surface 27 of photoresist material 25 that is in contact. with film 33. The flow rate of inhibitor 47 entering ports 39a and 39b is preferably selected to maintain a desired thickness of deadzone 41 along the build axis (z). As shown in Fig. 2, the build plane 32 is separated from the inhibitor-permeable film 33 along the build axis (z) by a distance that defines the thickness of the dead zone 41. When energy is projected solidification from the pattern generator 37, the solidification starts at the construction plane 32 and does not occur in the dead zone 41.

Inhibitor permeable film 33 may have a tendency to fall into a window 48. In some implementations, a displacement detector is provided that tracks position, in the build axis (z), of a point (for example, a center point "C") on the film 33 within the window 48. A feedback control system may be implemented that adjusts the flow rate or pressure of the inhibitor 47 entering or exiting inhibitor holes 39a and 39b to control the position of center point "C". Immersion depth 40 is the thickness of the build axis (z) between the exposed upward facing surface 30 of the photoresist material and the build plane 32. Immersion depth 40 is the depth at which the downward facing surface formed most recently the object 24 is immersed in the unsolidified photoresist material 25. In other examples, the displacement of the film 33 is controlled by adjusting the rate of upward movement of the build platform 26 along the build axis (z). In further examples, the flow rate or pressure of the inhibitor 47, on the one hand, and the speed of the build platform 26, on the other hand, are used to control the displacement of the center point C of the film 33. For example, one can use a split-gap control system in which the inhibitor pressure in chamber 46 (Figs. 1B, 1C, and 2) is adjusted to control film travel until it reaches a high limit, and then the speed The build platform 26 can be adjusted to control the displacement of the film 33 as needed once the inhibitor pressure limit is reached.

Referring to Fig. 3, another example of container 28 is provided. In this example, container 28 comprises sidewalls 38 defining a frame that holds inhibitor-permeable film 33 in place. An inhibitor permeable film 33 defines the bottom 36 of the container 28. The inhibitor 47 flows through the inhibitor permeable film 33 and into the photocurable material to create the dead zone 41 which is defined between the build plane 32 and the film. inhibitor permeable 33. The temperature of dead zone 41 can also be adjusted to prevent solidification from occurring in dead zone 41.

Referring to Fig. 4, another example of a photoresist container 28 is provided. In this example, the bottom of the container 28 is defined by a rigid or semi-rigid transparent panel 36 to which a transparent microfluidic PDMS (polydimethylsiloxane) 35 has been laminated. Inhibitor 47 (eg, air or oxygen) enters the microfluidic PDMS 35 from the sides (the thickness dimension) and is then transported up along the build axis (z) into the photoresist material 25. In this example and those of Figs. 2 and 3, the rigid or semi-rigid transparent solidification panel 36 is impermeable to the inhibitor 47 (unless entry ports such as ports 39a and 39b in Fig. 2 are provided).

Regardless of which container 28 is used, in each case the pattern generator 37 projects a series of images onto the lowest surface 27 of the photoresist material 25. The images pass through the transparent, rigid or semi-rigid panel 36 (if present). and inhibitor permeable film 33 or microfluidic PDMS layer 35 towards photoresist 25. Due to the presence of inhibitor 47, dead zone 41 is created and solidification occurs in the build plane 32 instead of the surface. lower surface of photohardening material 27.

The system 20 for manufacturing three-dimensional objects from a solidifiable material 25 can be operated in a batch or continuous mode. In the batch mode, immediately prior to the formation of a layer of object 24, the exposed downward facing surface 29 of object 24 is positioned as illustrated in Fig. 1B. The downward facing exposed surface 29 is separated from the construction plane 32 by a layer thickness Az. In the batch mode, the build platform 26 and the downwardly facing exposed object surface 29 are stationary at this time. The pattern generator 37 then projects a two-dimensional solidification energy pattern upward along the build axis (z) through the rigid or semi-rigid transparent panel 36 and through the inhibitor-permeable film 33 and bottom surface. 27 of photoresist material 25. The exposure time per image is defined as the variable t ^e and is selected to solidify the photoresist material 25 to the selected layer thickness Az given the intensity of the projected solidification energy.

The energy pattern passes through the dead zone 41 without solidifying the photoresist 25 in the dead zone 41 due to the inhibitor 47. Once the energy pattern passes into the build plane 32, it solidifies the photoresist 25 at a layer thickness Az (shown exaggerated in Fig. 1C). Next, the build platform 26 is raised along the build axis (z) a distance W where W > Az. The build platform 26 is raised this distance to facilitate the flow of photoresist material into the space between the exposed downward facing surface 29 of the object 24 (FIG. 1B) and the film 33 (or PDMS layer 35). After being held in the raised position for a period of time, the build platform 26 lowers a distance W-Az and the next layer solidifies. Therefore, during batch mode operation, the build platform 26 is stationary when solidification energy images are projected onto the photoresist 25. In contrast, when the build platform 26 moves in the batch mode, the solidification energy is not projected at a level sufficient to cause the photoresist material 25 to solidify.

System 20 can also be operated in a continuous mode. In the continuous mode, the build platform 26 moves along the build axis (z) while the pattern generator 37 projects solidification energy images onto the photoresist material 25. In addition, the pattern generator 37 continuously projects freeze energy images (except for any image switching delay that occurs due to limitations of the pattern generator 37). The projected images will have a time exposure t ^e associated with them. The exposure time t ^e is the time during which any image is projected. However, an identical image may be projected repeatedly for portions of a given object, in which case that image may be projected for a multiple of the exposure time t ^e. The layer thickness Az defined for the batch mode of operation defines an incremental distance along the build axis (z) between images successively projected by the pattern generator 37 during the continuous mode. The incremental distance between consecutive image exposures Az can be related to the speed of movement of the build platform 26 along the build axis (z) and the exposure time t ^e as follows.

where Az = change in build platform position between consecutive image exposures (microns, p);

dz/dt = velocity of the build platform along the build axis (p/s);

t ^e = exposure time per image (s).

When the layer thickness Az is fixed, the required build platform velocity dz/dt for a given exposure time can be calculated by rearranging equation (1) as follows:

A bitmap or other data representation (such as a voxel data set) of each layer will define the image projected by pattern generator 37. Thus, each bitmap will correspond to a layer index k defining a position on the construction axis (z). The bitmaps or other data files used to start the exposure by the pattern generator 37 toggle every ^t seconds. If you are forming a region of the object where the cross-sectional area does not change, you do not need to switch the bitmaps. Instead, the same bitmap can be used for a selected number of kx periods during a total aggregate exposure time of k ^x t ^e , where k ^x is also equal to the number of consecutive identical layers, and t ^e is the exposure time. exposition.

An advantage of providing a dead zone 41 is that the most recently solidified section of object 23 (FIG. 1C) does not have to be separated from the bottom 36 of the container for photoresist material 28 or the film 33 (or any surface with which the photoresist material adheres). 25 stay in touch). Because of this, the system 20 can be operated in continuous mode throughout the object construction process. However, it has been found that when the object 24 has a maximum cross-sectional area (perpendicular to the build axis (z)) that exceeds a certain threshold, if the build platform velocity dz/dt is too high, the The amount of inhibitor 47 in the dead zone 41 may increase, causing the dead zone 41 to increase in height along the build axis (z). If this happens, channels may form in the object 24 and/or delamination may occur. As a result, the speed dz/dt of the build platform along the build axis must be reduced to a value that allows the layers with the largest cross-sectional area to form properly and dead zone expansion is avoided. 41, which can slow down the entire build process.

It has been discovered that by operating the system 20 in an alternating sequence of continuous and batch modes, the total time required to fabricate a three dimensional object 24 can be reduced relative to a scenario where the continuous mode is used throughout the process. object formation. At a given build platform speed dz/dt , periodic switching to a batch mode has been found to prevent depletion of the photohardening inhibitor in the dead zone 41 in regions of the objects having cross-sectional areas exceeding certain thresholds.

In certain examples, if the largest continuous cross-sectional area of the three-dimensional object is less than about 0.5 cm2, preferably less than about 1.0 cm2, and more preferably less than about 1.5 cm2, the mode of operation continuous is used throughout the manufacturing process of the three-dimensional object.

In other examples, continuous and discontinuous modes of operation alternate at a frequency that depends on the largest cross-sectional area of the object. In the same or other examples, the frequency at which the modes switch increases as the largest cross-sectional area of the object increases.

In one scenario, if the largest continuous cross-sectional area of the three-dimensional object is at least about 1.5 cm2, the continuous and discontinuous modes alternate at least every ten layers, preferably at least every eight layers, and more preferably , at least every five layers. In the same or other examples, if the largest continuous cross-sectional area of the three-dimensional object is at least about 2.0 cm2, preferably at least about 2.2 cm2, and more preferably at least about 2.5 cm2 roughly, the continuous and discontinuous modes alternate at least every five layers, preferably every four layers, and more preferably every three layers.

Referring to Fig. 5, a flow chart is provided illustrating a method for forming a three-dimensional object using alternating continuous and batch modes of operation. In step 1010, object data (such as provided in .stl files, bitmap files, or voxel data files) is read and the area with the largest cross-section (perpendicular to the construction axis ( z)) on the object. A desired layer thickness Az is then read from the appropriate data file at step 1012. Thinner layer thicknesses provide better resolution and smoother, more accurate parts. However, as the layer thickness decreases, the total time required to complete the construction of an object increases. In certain examples according to the present disclosure, the Az layer thickness is at least about 20 microns, preferably at least about 30 microns, more preferably at least about 40 microns, and even more preferably at least about 45 microns. . In the same or other examples, the Az layer thickness is no more than about 80 microns, preferably no more than about 70 microns, more preferably no more than about 60 microns, and even more preferably no more than about 55 microns.

In step 1014 an initial velocity dz/dt of the build platform along the build axis (z) is read. The speed of the build platform is initially chosen to maintain the photoresist inhibitor permeable film 33 in a substantially flat condition. Depending on the selected layer thickness Az and the speed ( dz/dt) of the build platform, an exposure time t ^e can be calculated, which is the moment when the pattern generator 37 projects an image for a value of given layer index (k=1 to K ^max ) on the surface of the photoresist material facing the pattern generator 37 (eg, the surface of photoresist material 25 in contact with the film 33 or the microfluidic PDMS 35).

In preferred examples, system 20 switches between continuous and discontinuous modes of operation at a switching frequency that is dependent on the largest cross-sectional area of the three-dimensional object being built. Multiple area thresholds can be used to define multiple switching frequencies. In the procedure of Fig. 5, two area thresholds are used: 2.5 cm ² and 1.5 cm ² . Each area threshold defines a different switching frequency between continuous and discontinuous operation. The larger area triggers a higher switching frequency (ie fewer layers before mode switching). At step 1018, the maximum cross-sectional area A ^max of the object is compared to the highest area threshold of 2.5 cm ² . If the object has a cross-sectional area that is greater than 2.5 cm ² anywhere along its build axis height (z), control is transferred to step 1024, where it is first used continuous mode. At step 1024, the build platform 26 continuously moves up along the build axis (z) as the images are exposed. Although not shown, a timer may be provided (in software) to determine the elapsed operating time once the build platform 26 begins to move along the build axis (z). At step 1024, each time an exposure period t ^e elapses in the timer, a period counter ( IP ^e ) is incremented and a check is made at step 1026 to determine if the last layer of the object has solidified ( that is, k = K ^max ). If the last layer has solidified (ie, step 1026 returns a value of "YES"), the procedure ends. During step 1024, pattern generator 37's image projection is uninterrupted (except for delays caused by hardware or software limitations in pattern generator 37 when the projected image changes), and build platform 26 moves smoothly. continues up along the construction axis (z). Instead of starting with continuous mode, as shown in Fig. 5, an object build could start with discontinuous mode. Also, in some implementations, a series of "record" layers are created at the beginning of the object build process to better adhere the object 24 to the build platform 26. By fabricating the record layers, the exposure time can be increased. (or intensity can be increased if possible) to overcure layers to a layer depth greater than Az.

In preferred examples, during continuous mode of operation, photoresist inhibitor 47 continues to permeate film 33 and maintain dead zone 41 preferably at a substantially constant build axis height (z), to ensure that photoresist material 25 solidifies. enough to connect each layer to the previous layer of the object. In certain preferred examples, the displacement of the film 33 is monitored using a displacement detector, and the pressure of the photoresist and/or the speed dz/dt of the build platform are manipulated to keep the film 33 substantially flat. In the case of a microfluidic PDMS layer 35 (FIG. 4) laminated to a rigid or substantially rigid panel 36, displacement of the microfluidic PDMS layer 35 is not a problem.

The switching frequency when the cross-sectional area is greater than 2.5 cm ² is three (3) layers. Therefore, step 1028 determines if the continuous procedure has been carried out for three layers by dividing the sum of the elapsed exposure periods ZP ^e /3 by 3 to determine if the result is 1 (assuming that P ^e was initialized to zero when step 1024 began). Each time the exposure time t ^e elapses, the number of IP exposure periods ^e is increased by one. Therefore, if an exposure time t ^e of two (2) seconds is used, each time an additional two seconds elapses, the number of exposure periods IP ^e is increased by one. Therefore, at step 1028, after three exposure periods have elapsed, the value of ZP ^e /3 will have a value of 1, causing step 1028 to return a value of "YES".

When step 1028 returns a value of YES, control is transferred to step 1030 to begin the batch mode of operation. As mentioned above, during the batch mode of operation, the pattern generator 37 projects solidification energy images onto the downward-facing surface 27 of photoresist material 25 only when the build platform 26 is stationary. After each layer solidifies, the build platform 26 is raised a distance W, which is greater than the layer thickness Az, to allow the unsolidified photoresist material 25 to fill the space between the downward-facing surface 29 of the object 24 and movie 33 (FIG. 1B).

Step 1032 is performed after each layer solidifies to determine if the object is complete (ie, k = K ^max ). If the object is complete, the procedure ends. Otherwise, step 1034 is performed to determine if the switching frequency of three (3) has been reached (i.e., ZP ^e /3 is 1, assuming ZP ^e was initialized to zero at the beginning of step 1030). If the switching frequency of 3 has been reached, control is transferred to step 1024 and the process continues.

If the area threshold of 2.5 cm ² is not exceeded, step 1018 returns a value of NO and control passes to step 1020. At step 1020, the largest cross-sectional area A ^max of object 24 it is compared with a threshold value of 1.5 cm ² . If step 1020 returns a value of YES, control is transferred to step 1036 and the continuous mode of operation is initiated. Stages 1036, 1040, and 1044 function in the same manner as stages 1024, 1026, and 1028, respectively, except that the switching frequency in stage 1044 is five (5) layers. Therefore, at step 1036, the continuous operation mode is started, and each time an exposure period P ^e elapses, it is determined whether the construction of the object is finished. Step 1040. If the construction of the object is complete, step 1040 returns a value of YES and the procedure ends. Otherwise, control is transferred to step 1044 and the number of elapsed periods P ^e in the current continuous mode of operation is divided by the five (5) layer switching frequency. If IP ^e /5 is not one (step 1044 returns a value of NO), control is transferred to step 1036 and the current continuous mode continues. If IP ^e /5 is one (assuming ZP ^e is initialized to zero when step 1036 begins), step 1044 returns a value of YES and control is transferred to step 1038 to begin the batch mode of operation, which is performed as described in step 1030. After each layer is formed, step 1042 determines whether the object is complete (ie, k=K ^max ). If step 1042 returns a value of YES, the procedure ends. Otherwise, control passes to step 1046 to determine if the mode switching frequency (five) has been reached. If reached, control is transferred to step 1036 to switch to the continuous mode of operation. If step 1046 returns a value of NO, control is transferred to step 1038 to continue the current batch mode of operation.

If step 1020 returns a value of NO, then the largest cross-sectional area A ^max is below a threshold where mode switching occurs and a continuous mode can be used for the entire object. In that case, control is transferred to step 1022 to enter a continuous mode of operation. After each exposure period P ^e , step 1025 determines if the object is complete. If step 1025 returns a value of YES, the procedure ends. Otherwise, continuous operation mode continues.

EXAMPLE 1

The use of switching between modes, such as in the exemplary procedure of Fig. 5, allows objects whose maximum cross-sectional area exceeds certain thresholds to be built more quickly than would be the case if a continuous mode were used. throughout the construction of the object. This is the case because the build platform velocity dz/dt is constant throughout the object build and must be set low enough to form the largest continuous cross-sectional area A ^max without exhausting the dead zone 41 .

An object is built in 50 micron layers (ie Az = 50p) using (i) an entirely continuous mode of operation and (ii) switching between modes. The object is built using both techniques on the same system 20 and has a larger continuous cross-sectional area of 2.5 cm2. In order to avoid expansion of the dead zone 41, the exposure time t ^e is set to 15 seconds, which produces a velocity ( dz/dt) of the build platform along the build axis of 50/ 15 = 3.33 p/s. In other words, during the continuous mode of operation, it takes 15 seconds for the build platform 26 to travel 50 microns. The speed is maintained in the formation of the entire object.

By using mode switching with a mode switching frequency of five (5) layers (of 50 p each) and a post-solidification offset W of 3 mm, the exposure time t ^e can be set to 3- 5 seconds. In batch mode, each layer takes approximately 10-12 seconds to build, which includes moving the build platform the distance W to W-Az, solidifying the layer, and separating the object from the layer. In both passes (i) and (ii) the same pressure of oxygen (inhibitor) is used. Using mode switching, the object is completed in 57 minutes. By continuously moving throughout the construction, the object is completed in 2 hours and 4 minutes. As a result, switching between modes allows the object to be built significantly faster than would be the case if only continuous or only discontinuous operation were used.

Referring now to Figs. 6, 7 and 10, another method for preventing excessive expansion of the dead zone 41 will now be described, which does not form part of the present invention.

According to the method, object-independent continuous regions within a layer having different values of surface area and slenderness are exposed to solidification energy for different exposure times. An "independent continuous region" is a region of an object layer in the x-y plane that is uninterrupted and not connected to another region of the object in that layer. A bitmap can be used to graphically represent image data by plotting the intensity of pixels at different x-y locations for a layer. According to the procedure, geometric parameters are identified that indicate that the size and shape of the object can cause fluid disturbances that result in a pressure drop around the periphery of the object unless the platform velocity is reduced. of construction 26 and the exposure time is increased. In general, the parameters are used to select those independent continuous regions that require slower build platform speeds and longer exposure times, which in turn dictates which independent continuous regions are examined to determine an exposure time. A variety of different parameters can be used. Three parameters discussed below are surface area, slenderness or inverse slenderness, and the ratio of internal void area to external boundary area.

The "surface area" is the area in the x-y plane of the independent continuous region defined by the outer boundaries of the area (ie, the inner void areas are not subtracted). As used herein, the term "surface area" is synonymous with "outer boundary surface area." As is known in the art, the larger an area that pushes against a fluid, the greater the pressure. As the surface area increases (whether there are no voids or in a constant void area), the pressure at the perimeter of the three-dimensional object decreases, causing a pressure drop between the photohardening inhibitor supply and the object, which results in an increase in inhibitor flow rate. "Slenderness" (represented as "G" herein) is the ratio of the surface area of an independent continuous region to the length of the region's perimeter. Slenderness reflects the fact that for a given object area, objects that are substantially larger in one dimension relative to others can create fewer fluid disturbances when moving in a volume of solidifiable material. "Inverse slenderness" can also be used, and as referred to herein, is defined as the square of the length of the contour of an independent continuous region divided by the surface area of the region. The term "slenderness criterion" encompasses both slenderness and inverse slenderness. In certain examples herein, surface area, slenderness (or inverse slenderness), and the ratio of internal void area to external boundary area are used to determine whether to include an independent continuous region in a set of regions. used to determine an exposure time. The parameters are compared to various criteria to make this determination.

Although large surface areas can affect the required exposure time and the speed of the build platform, the situation may be different for an independent continuous region with a significant amount of void space in it because the solidifiable material can flow through. the holes. Thus, the ratio of the sum of the internal void areas in an independent continuous region to the external boundary surface area of the region (sometimes called the "void ratio" or "ratio" herein) is also described herein as a geometric parameter used to determine whether a particular independent continuous region should be considered when determining an exposure time or build platform speed. A low ratio indicates that the region should be included. In FIG. 7, bitmap n has four independent continuous regions. The four independent continuous regions solidify during an exposure time t ^e . Two of them solidify during an accumulated exposure time of t ^e + t ⁿⁱ , and one of them solidifies during an accumulated exposure time of t ^e + t ⁿⁱ + t ⁿ 2 . In addition, the build platform 26 moves during a dead time t ^d while insufficient solidification energy is projected to solidify the solidifiable material. Therefore, as shown in Fig. 6, for a single object layer having thickness Az, the build platform travels a distance Az along the build axis for a cumulative time t ^d + t ^e + t ⁿⁱ + t ⁿ² . Therefore, the speed of movement of the build platform 26 along the build axis (z) is dz/dt = uz/ ( td + ^{t e} + t ⁿⁱ + tn ² ). As described above, when certain containers of solidifiable material are used, such as container 28 of Fig. 1B, the pressure of inhibitor in chamber 46 can be adjusted to keep film 33 substantially flat. Furthermore, if the pressure reaches a high or low limit, the speed of movement of the build platform 26 along the build axis (z) can be adjusted to keep the film 33 substantially flat. In such cases, if the speed of the build platform 26 is adjusted, the dead time t ^d is also preferably adjusted to keep the layer thickness A z constant.

In preferred examples, the dead time t ^d is determined by the slenderness (or inverse slenderness) of a given subset of independent continuous regions D. In the same or other examples, t ^e is determined as a function of the composition of the solidifiable material used and may be indicated by a material identifier in a database associated with system 20. In the same or other examples, subset D is a set of independent continuous regions that satisfy a surface area (>St ² ) criterion, a criterion slenderness (>Gt) or inverse slenderness (<G't), and a ratio of internal void area to external boundary area ( <r ^t ). The set of independent continuous regions D used to determine the dead time t ^d can be defined as follows:

where D ⁱ is an element of the set D of independent continuous regions of a layer used to determine a dead time t ^d for the layer;

j is an index ranging from 1 to j ^max that identifies those independent continuous regions Di that belong to the set D ;

G ^ai is the slenderness of the independent continuous region i of the current layer (mm);

G ^t is a slenderness threshold used to determine the set D (mm);

G ^'ai is an inverse slenderness of the independent continuous region i (dimensionless);

G't is an inverse slenderness threshold used to determine the set D;

^rt is the void ratio threshold used to determine ^D¡ ;

i is an index that identifies the independent continuous region among all the independent continuous regions in the layer.

The dead time is determined as a function of the maximum slenderness or the minimum inverse slenderness of the set D, that is:

( 4) td= f ( Gmax ( D) O ( ¡ 'min ( D))

Appropriate dead times t ^d are determined experimentally and stored in a process computer database that relates them to G max or G min.

An alternative procedure for determining the dead time t ^d for a layer of a three-dimensional object will now be described with reference to Fig. 13. According to the procedure, a dead time for each independent continuous region t ^di is determined for each layer , and the maximum value of the dead times t ^di for the independent continuous regions is selected as the layer dead time t ^d . Referring to Fig. 13, the surface area thresholds A ¹ and A ² are experimentally determined and used to define three surface area regimes for a given independent continuous region i . In the first regime, the independent continuous region surface area A i is greater than zero and not greater than the first surface area threshold A ⁱ . In the second regime, A ⁱ is greater than the first surface area threshold A ¹ and not greater than a second surface area threshold A ² . In the third regime, Ai is greater than A ^2.

If the independent continuous region surface area A ⁱ is greater than zero and not greater than A ⁱ , the dead time for that region t ^di is zero regardless of the values of the slenderness, inverse slenderness, or ratio of internal void area to relative to the external contour area ("void ratio").

If the independent continuous region surface area A ⁱ is greater than the first threshold surface area A1 and not greater than the second threshold surface area A ² and the inverse slenderness value G ^¡ for the region is greater than zero and less than the first inverse slenderness threshold G ⁱ , the dead time for the region t ^di is zero. If the inverse slenderness for region G' ⁱ is greater than the first inverse slenderness threshold G ⁱ , then the region dead time t ^di depends on the value of the region's void ratio (i.e., the area ratio of internal void with respect to the external contour area). If the void ratio for region R ⁱ is greater than zero and not greater than a first void ratio threshold R ⁱ , the region dead time has a first non-zero value t ^di ( 1 ) . If the void ratio for region R ⁱ is greater than the first void ratio threshold, the dead time for region t ^di is zero.

If the independent continuous region surface area is greater than the second threshold surface area A ² , and the inverse slenderness for the region G , is greater than zero and not greater than a second inverse slenderness threshold G2 ^, regardless of the value From the void ratio, the dead time for the region will have a non-zero value t ^di ( 2 ) . If the inverse slenderness for the region G ⁱ is greater than the second inverse slenderness threshold and not greater than a third inverse slenderness threshold G ³ , the dead time for the region will have a nonzero third value t ^d ¡ ( 3 ) , where t ^d ¡ ( 3) is less than t ^di ( 2). If the inverse slenderness for the region is greater than the third inverse slenderness threshold G ^{3 ,} and the void ratio R ^¡ is greater than zero and not greater than a second void ratio R ² , the dead time for the region t ^di will have a fourth non-zero value ^t d¡ ( 4 ) , where t ^d¡ ( 4) is less than t ^d¡ ( 2) and t ^d¡ ( 3). However, if the void ratio for region R ⁱ is greater than the second void ratio threshold R ^{2 ,} the dead time is zero. Therefore, the table in Fig. 13 defines the dead time of an independent continuous region of an object layer as a continuous function of the surface area ^A¡ , the inverse slenderness G'¡ ^, and the void ratio ^R¡ of the region.

To determine the exposure time t ⁿⁱ , a first subset H of independent continuous regions is identified. The set H is defined by those independent continuous regions that satisfy a surface area criterion ⁽ S ^t 3<S ^a £S ^t 4) ^, a slenderness criterion (>Gt ² ) or an inverse slenderness criterion ⁽ <G ^{t¿) ,} and a ratio criterion of the internal void area with respect to the external contour area (<rt ² ). The set of all independent continuous regions H used to determine the exposure time t ⁿⁱ is defined as follows:

where H is an element of the set H of independent continuous regions of a layer used to determine an exposure time t ⁿⁱ ;

Sa ⁱ is the surface area of the independent continuous region i in a current object layer (mm2);

G ^a, is the slenderness of the independent continuous region i (mm);

G ^t2 is the slenderness threshold used to determine the set H (mm);

G' ^a ¡ is the inverse slenderness of the independent continuous region i (dimensionless);

G' ^t2 is the inverse slenderness threshold that can be used to determine the set H (dimensionless); and m is an index ranging from 1 to m ^max that identifies those independent continuous regions H ⁱ that belong to the set H.

The maximum surface area in the set H can be defined as S ^max ( H). The maximum value of slenderness in the set H can be defined as G ^max ( H). The minimum inverse slenderness can be defined as G' ^min ( H). The value of the exposure time t ⁿⁱ for the first object data subset in the layer is a function of the maximum area and maximum slenderness in the set H and the solidifiable material (identified by an ID from a database). Therefore, t ⁿⁱ can be defined as follows:

( 6)tni=f ( GMax ( H) OG'Mm( H),ID,Smax ( H))

where t ⁿⁱ is an exposure time (s) for the 1-subset of the current layer's independent continuous regions;

ID is a text identifier that identifies the solidifiable material;

S ^max ( H) (mm2) is the maximum surface area in the set H;

G ^Max(H) is the maximum slenderness value in the set H (mm);

G ^'Min ( H) is the minimum value of inverse slenderness in the set H (dimensionless).

Similarly, a second subset R of independent continuous regions is identified that has a surface area ^S a i that exceeds the fourth threshold:

( 7) Ri ( n=la Ttmax) £ ( S ^t4 < Sai, (( Ga¡ > Ga) or ( G'm <G'a)) and relation <rts}

where R ^¡ is an element of the set R, which is the set of independent continuous regions used to determine the second exposure time of subset t ⁿ² . The value of the exposure time t ⁿ² of the second subset of object data in the layer is a function of the maximum area and the maximum slenderness G ^max ( R ) or the minimum inverse slenderness G ^{' min} ( R ) in the set R. For Therefore, t ⁿ² can be defined as follows:

( 8) tn2 = f ( G max ( R ) OG 'min ( R ), ID, ^Smax ( R ) )

where t ⁿⁱ is an exposure time (s) for the subset 2 of the independent continuous regions of the current layer;

ID is a text identifier that identifies the solidifiable material;

S ^max ( R) (mm2) is the maximum surface area in the set R;

G ^max ( R) is the maximum slenderness value in the set R.

G' ^min ( R) is the minimum slenderness value in the set R.

As shown in Fig. 7, a single layer is exposed using multiple bitmaps. Bitmap n includes all independent continuous regions of a layer, and the solidification energy is projected into the build region 32 of solidifiable material 25 for the entire layer exposure time t ^e using bitmap n. Bitmap n1 is a first subset of bitmap n, and the solidification energy is projected onto the build region 32 according to bitmap n1 for an exposure time of t ⁿⁱ . Bitmap n2 is a second subset of bitmap n and is also a subset of bitmap n1, and solidification energy is projected into build region 32 in accordance with bitmap n2 for an exposure time of t ⁿ² .

Referring to Fig. 10, there is shown a method, which is not part of the present invention, for manufacturing a three-dimensional object by solidifying a solidifiable material. The method involves the use of a dead zone provided by a source of photoresist inhibitor 47 entering a volume of the settable material 25 by impregnation of a permeable layer of photoresist inhibitor 33. The inhibitor 47 enters a surface of the settable material at an interface 27 between the settable material 25 and the photoresist inhibitor permeable layer 33. The exemplary system 20 can be used with any of the settable material containers of Figs. 2-4, for example.

At step 1050, the object data is read by a process computer for the entire object. This can also occur one layer at a time rather than as a single stage. The selected Az layer thickness that defines the resolution of the object is read at step 1052. At step 1054, a material ID ("ID") that identifies the solidifiable material is read.

In certain examples, a database is maintained in computer-readable storage operatively connected to a process computer associated with system 20. The database relates solidifiable material identifiers (IDs) to full layer exposure times by curing depth unit f ^e /Az. Step 1056. Full layer exposure times per unit depth of cure f ^e /Az are determined experimentally for each ID by projecting solidification energy over a specified area and are related to each other in a database to which accesses the process computer. At step 1058, the layer index k is initialized to a value of zero. The layer index uniquely identifies a position along the build axis (z) where solidification occurs. The layer index is incremented by one at step 1060.

For the current layer (defined by the current value of k), the surface area ^S a i of each independent continuous region is determined at step 1062. The index i uniquely identifies each independent continuous region in the layer. If none of the independent continuous regions have a surface area that exceeds a first threshold ^Sfi (step 1064), control is transferred to step 1066 and continuous mode is used for the entire layer. In continuous mode, a bitmap defining the entire layer is used during the exposure time f ^e as the build platform 26 moves along the build axis (z) at a speed equal to Az/ f ^e . When the layer is complete (ie, when the build platform 26 has traveled the distance Az), control is transferred to step 1060 to start the next layer. Therefore, for layers with relatively small independent continuous regions, a single exposure time f ^e can be used with a full layer bitmap (bitmap n).

If in step 1064 at least one independent continuous region of the layer has a surface area S ^ai that exceeds the first threshold value of S ^fi , in steps 1068-1094 the multiple bitmap procedure exemplified by Figs. . 6 and 7. A set of independent continuous regions D for which the surface area S a ⁱ exceeds a second threshold surface area S f ² (which may be the same value as S ^fi ) is identified (step 1068). Set D is the set of regions that will be used to determine the dead time f ^d.

The above procedure is only used for those layers that have at least one independent continuous region with a surface area that exceeds a first given threshold. Otherwise, the layer solidifies according to the layer data for the entire layer during an exposure time f ^e as the build platform moves continuously at a speed of dz/df = Az/f ^e (step 1066). It has been found that by slowing the movement of the build platform 26 (increasing the cumulative exposure time), the reduction in pressure at the periphery of the object relative to the location where the inhibitor 47 enters the settable material 25 decreases, which causes the pressure drop and inhibitor flow rate in the settable material 25 to decrease relative to what would be the case if the build platform moved at a continuous speed. Decreasing (or avoiding increasing) the flow rate of inhibitor 47 prevents expansion of dead zone 41 and reduces the likelihood of channeling through the object and delamination of the object.

The "full layer" exposure time f ^e is an exposure time during which all regions of the curable material to be solidified solidify. In preferred examples, f ^e is selected based on the settable materials that are used. In certain examples, system 20 includes a computer with a database that relates values of f ^e to material identifiers ID.

For those layers with at least one independent continuous region with a surface area that exceeds the first threshold, the bitmap is subdivided based on the surface area and slenderness of the various independent continuous regions. A first set of independent continuous regions D is identified, whose elements D ⁱ meet the criteria of equation (3). Each element D ⁱ of set D has an index i associated with it, and there are j = 1 a j ^max elements of set D. In step 1070, the dead time f ^d is determined. The dead time f ^d is a function of the maximum slenderness value ( G ^max ) or the minimum reverse slenderness value ( G' ^min ) for any of the independent continuous regions D ⁱ in the set D. In certain examples, the system 20 is operatively connected to a database that relates dead time values f ^d to maximum slenderness values G ^max ( D ) associated with surface areas S a ⁱ at or above a specified threshold S ^t2 . Dead time can be determined using a variety of different functions. For example, it could be a continuous or discontinuous function of the maximum surface area and the smallest inverted slenderness (or maximum slenderness) of the set D (for a given solidifiable material). Equation (4) (above) is merely exemplary. The table in Fig. 13 could also be used to determine the layer dead time f ^d as described above.

At step 1072, a first subset of independent continuous regions H (equation (5)) is identified that will define bitmap n1. An exemplary procedure for determining which elements H belong to the set H is provided by equation (5).

In step 1076, the first subset exposure time f ⁿⁱ is determined. The value of f ⁿⁱ can be determined in a variety of different ways using continuous or discontinuous functions of the surface area and the slenderness (or the inverted slenderness) of the independent continuous regions H that comprise the set H (for a given solidifiable material) . Equation (6) is an example. In equation (6), the first subset exposure time f ⁿⁱ is a function of the solidifiable material, the maximum slenderness or the minimum inverted slenderness, and the maximum surface area ^Smax of the independent continuous regions comprising the set H. The value of f ⁿⁱ is a function of the maximum slenderness Gmax ( H) or the minimum inverted slenderness G'min ( H) of the independent continuous regions in the set H, the solidifiable material (ID), and the maximum surface area Smax of any of the continuous regions independent in the set H (equation (5)).

At step 1078, a second subset of independent continuous regions R (equation (7)) is identified that will define bitmap n2. Each element R, has an index value i associated with it and has a surface area Sai that is above a fourth threshold St4.

In step 1082, the second subset exposure time tn ² is determined. The value of tn ² can be determined in a variety of different ways using continuous or discontinuous functions of the surface area and the slenderness (or the inverted slenderness) of the independent continuous regions R , that comprise the set R (for a given solidifiable material ). Equation (8) is an example. In equation (8), the second subset exposure time tn ² is a function of the solidifiable material, the maximum slenderness or the minimum inverted slenderness, and the maximum surface area Smax of the independent continuous regions R , comprising the set R In the example of Fig. 6, the change in position in the build axis (z) of the build platform 26 with respect to time is constant. Therefore, the speed dz/dt of the build platform can be calculated (step 1084) as follows:

( 9) dz/dt = Az/ ( td te luí h¡2j

where dz/dt is the speed of the build platform along the build axis (mm/s);

Az = layer thickness (microns)

td = dead time (seconds)

te= full layer exposure time (seconds)

tni= first subset exposure time (seconds)

tn ² = second subset exposure time (seconds)

At step 1086, the build platform moves during the dead time td during which the pattern generator 37 does not project sufficient setting energy to solidify the settable material 25. Next, at step 1088, the pattern generator projects the full layer bitmap (bitmap n of Fig. 7) over the full layer exposure time te, thus exposing all independent continuous regions of solidification in the layer. In step 1090, the first subset H and the second subset R of independent continuous regions are solidified during the first subset exposure time tni. In step 1092, the set R is exposed during the second subset exposure time tn ² .

If the last layer is complete, the layer index k will have reached its maximum value kmax, and the process ends (step 1094). Otherwise, control passes to step 1060 and the next layer is processed.

In some cases, the actuator and motor used to move the build platform 26 will be limited in the minimum build platform speed dz/dt they can achieve, causing you to be driven to a lower limit. In such cases, it is beneficial to stop the build platform 26 when the H and R subassemblies solidify during the first subassembly exposure time tni and the R subassembly solidifies during the second subassembly exposure time tn ² . Graphically, this would be represented by making the line in Fig. 6 horizontal during the exposure periods tn ¹ and tn ² . As mentioned above, if the speed of the build platform along the build axis (z) is adjusted to control the flatness of the film 33, the dead time td can be adjusted to keep the layer thickness Az constant.

EXAMPLE 2

PIC 100c, a filled thermoplastic material available from Envisiontec, Inc. of Dearborn, Michigan, is provided in a system similar to that of Fig. 1A with the settable material container 28 of Fig. 1B. The intensity of the DLP light source is 480 mW/(dm)2. The inhibitor is oxygen and chamber 47 is maintained at a pressure of approximately 0.015 Bar. The surface area threshold used to determine membership in set D ( St ² ) is 10 mm 2 . The surface area threshold used to determine set membership ( St3) is 56 mm2. In this example no value of St4 is used. A second subset R is also not used. The inverse slenderness threshold Gt is 1.8, and the void ratio threshold rt is 0.5, and is the same value used to determine membership in set D and set D. set H. Full layer exposure time is 6 seconds. The layer thickness Az is 0.05 mm.

In those independent continuous regions where the surface area is between St ² and St 3 , the dead time is t ^d =3 seconds, and the first subset exposure time trn is 0.5 seconds. In those independent continuous regions where the surface area is greater than 56 mm2, the dead time is 6 seconds and the first subset exposure time tni is 0.8 seconds. Sti is less than or equal to St ² and there are independent continuous regions where the surface area is greater than Sti.

Certain objects will include a "protrusion". As used herein, the term "outgoing pixels" refers to pixels at a specific x,y location that have a grayscale value that is greater than a pixel at the same x,y location in the layer. immediately preceding object. In the limiting case, the pixels defining a boss provide a surface that is separated along the build axis (z) from every other surface of the object and the build platform 26. In other words, it is a surface with a x,y region that is not connected to a previous object layer or to the build platform. In many cases, the layers of an object are "over-cured", that is, higher solidification energy is supplied than is required to achieve the desired layer thickness Az. For non-protruding layers, such over-curing tends to improve inter-layer adhesion. However, if the bottom surface of a boss is over-cured, the boss will distort because curable material that is not meant to set will. In cases where overcuring is used, it is desirable to employ a construction (z) axis offset for outgoing pixels. The construction axis offset is a number of bitmaps by which the grayscale value is shifted from a particular x,y location. For example, the x,y location of an outgoing pixel can be shifted by a bitmap so that when layer n is formed, the outgoing pixels are assigned the grayscale values of the bitmap for layer n . After the boss ends (that is, once the grayscale values for x,y defined by the current layer are less than or equal to those of the previous layer), the offset is no longer applied to the pixels they are assigned the grayscale value dictated by the currently operating bitmap. Referring to Fig. 7, when the bitmap n corresponds to a particular position in the build (z) axis and the corresponding layer index k, the offset in the build (z) axis will delay the solidification of the material solidifiable for a specified number of phase shift layers. The number of offset layers is chosen so that any excess curing does not affect the grayscale values of lower layers below the outgoing pixels. Therefore, in an example with an overhang with no layers immediately below it, where a 50 micron layer thickness is used and the layers are cured in excess of 200 microns, the offset will be four (4) layers. In some examples, a database may be provided with a system 20 that relates the offset in the build axis (z) to the strength of the solidification energy source (for example, the strength of the electromagnetic radiation provided by the pattern generator 37), the exposure time and the curable material.

Another method, which does not form part of the present invention, for preventing the expansion of the dead zone 41 using varying radiation intensities (provided, for example, by grayscale) will now be described with reference to Figs. 8-9 and 11. As is known in the art, certain spatial light modulators, such as digital light projectors and liquid crystal displays, have pixels that can transmit light intensities at values between 0 and a maximum intensity. Pixel values are typically called "grayscale" or "color values". Fig. 8 shows separate continuous regions 60, 62, 64 and 66 of an object layer, and Fig. 9 is a bitmap 68 displaying gray scale values for bitmap regions 70, 72 , 74 and 76 corresponding.

According to the procedure, for each layer the surface areas and slenderness values of each independent continuous region are determined. If the layer does not have at least one independent continuous region with a surface area that exceeds a first threshold S ^ti and a slenderness value that exceeds a first threshold G ^it , variable intensities are not used and the same intensity is projected towards all layers. independent continuous regions of the layer.

Different independent continuous regions of an object layer having different surface areas and different slenderness values solidify at different intensities but during the same full-layer exposure time t ^e . According to the procedure, each independent continuous region has a surface area ^Sa that will be in a particular "cell" ( bin) or range of surface area values. The surface area range and the maximum slenderness value of the independent continuous regions that fall within that range will determine the grayscale value. In one example, a database is provided in which the various cells have a plurality of slenderness values, each of which corresponds to a grayscale value for that cell. If the speed of build platform 26 is adjusted along the build axis (z) to control the flatness of film 33 (FIG. 1B), the exposure times of each pixel will change. To compensate for the changed exposure times, the grayscale values of all active pixels (all pixels with enough energy to cause solidification) can be adjusted to maintain a constant layer thickness Az.

An illustrative example of the above variable intensity method is shown in Fig. 11. In step 1096 the object data is read and the layer thickness is read in step 1098. A settable material identifier (ID) is read in step 1100. The material identifier determines the exposure time t ^e . System 20 may be operatively associated with a database relating exposure time values t ^e to various materials identified by an identifier ID (eg, an alphanumeric string).

The layer index k is initialized to a value of zero (step 1104) and then incremented by one (step 1106). The surface area ^S a i of each independent continuous region (identified by the index i ranging from 1 to i ^max ) in the layer is determined (step 1108). If none of the independent continuous regions has a surface area ^S a i that exceeds a first threshold S ^ti , the layer solidifies in a continuous mode in which the build platform 26 moves continuously at a substantially constant speed dz ^/ dt upwards along the build axis (z) as the pattern generator 37 projects a pattern of solidification energy corresponding to all independent continuous regions during the process. exposure time t ^e . The solidification energy is projected with a constant intensity through the layer and, in some examples, with the full intensity of the pattern generator 37. The speed at which the build platform moves dz ^/ dt is the layer thickness Az divided by the exposure time t ^e . Once the layer is complete (at the end of t ^e ), control is transferred to step 1106 to start another layer.

In step 1110, if at least one of the independent continuous regions in the layer has a surface area ^Sa i that exceeds a first threshold S ^ti and a slenderness that exceeds a first slenderness threshold G ^t or is less than a first reverse slenderness threshold G' ^t , variable intensity solidification is used. Although not shown separately in Fig. 11, an additional step is preferably provided between steps 1110 and 1114 for calculating an initial velocity dz ^/ dt of the build platform. In the example, the initial velocity dz ^/ dt is a function of the surface area, inverse slenderness, and void ratio of each independent continuous region. According to the example, a build platform velocity is determined for each independent continuous region based on these parameters, and the minimum velocity determined for all independent continuous regions in the layer is used as the initial velocity. As mentioned above, this initial speed can be adjusted to control the flatness of film 33 (FIG. 1B). In one example a data table very similar to that in Fig. 13 is used, except that the row of dead time t ^di is replaced by a row of reference build pad speed dz ^/ dt (no dead time is used). dead in this example). After the speed of the reference build platform is determined (after a value of YES at step 1110), control is transferred to step 1114, where the values of S a ⁱ of each independent continuous region are assigned to cells (intervals of values from S to ^i). Cells are represented as X ^q , where q ⁼ 1 to q ^max . Each cell has a plurality of maximum slenderness values, each of which corresponds to a grayscale value GS ^{a =} f ( G ^max ( X ^{q )} ). Thus, for each independent continuous region, the cell X ^q to which it belongs and the maximum slenderness value of all the regions within that cell will determine the grayscale value used for the region:

( 10) GSi=f ( Gmax ( Xq) OG 'nnn ( Xq)

where GS ⁱ is the grayscale value applied to the independent continuous region i ;

X ^q is the cell to which the independent continuous region i belongs based on its surface area ^S a i ;

G ^max ( X ^q ) is the maximum slenderness value of the cell X ^q to which region i belongs for all independent continuous regions i ⁼ 1 ai ^max in the layer; Y

G' ^min ( X ^q ) is a minimum inverse slenderness value of the cell Xq to which region i belongs for all independent continuous regions i=1 at i ^max in the layer.

At step 1118, all independent continuous regions in the current layer are exposed to an intensity judged by their gray scale value. A check is made to determine if the last layer has solidified (step 1120). If so, the procedure ends. Otherwise control is transferred to step 1106 and the next layer is processed. The GSi grayscale values are not necessarily the final grayscale values used by the pattern generator. Instead, they are contributions to the final grayscale value for the purpose of controlling dead zone 41. The final grayscale value may have other contributions based on light intensity compensation (i.e., using values gray scale to adjust for variations in incident intensity in the x,y plane) and based on the shape of the part.

In FIG. 11 the grayscale values are step functions of the surface areas of the independent continuous regions and vary with the maximum slenderness value of all regions i that lie within each surface area stage. However, each continuous or discrete grayscale value function could also be determined for each region i based on the surface area ^S a i and the slenderness G ⁱ of the region.

In certain examples, the value of GS ⁱ for each region may be based on surface area, inverse slenderness, void ratio, and build platform speed. An example using this technique will be described below.

EXAMPLE 4

A filled thermoplastic material supplied under the tradename PIC 100c by Envisiontec, Inc. of Dearborn, Michigan, is used as the settable material. A DLP® is provided as a pattern generator and includes a 750 mw/(dm)2 light source. The intensity projected onto the solidifiable material will differ and can vary across the construction plane based on the use of grayscale. An n-1 layer includes three independent continuous regions, A, B, and C. Using a table, such as that in Fig. 13 (with total layer exposure time t ^e replacing dead time t ^d ), one can determine a full layer exposure time t ^e based on each individual independent continuous region AC. Based on the selected layer thickness Az, a dictated build platform speed can be determined for each individual independent continuous region, and the minimum speed is selected as the initial build platform speed for layer n. Using that speed, the surface area of each independent continuous region, the inverse slenderness of each independent continuous region, and the void ratio of each independent continuous region, a gray value can be determined for each GS¡ region.

An example table used to determine build platform speed is shown in Fig. 14A. The table relates surface area (Sai or Ai ^), inverse slenderness ⁽ G'i ⁾ , and void ratio (Ri) to build platform velocities ⁽ dz ^/ dt ⁾ , shown as divided Az layer thicknesses by the exposure times ⁽ t ^{e )} for the entire layer (there are no separately exposed subsets in this example).

Each region A, B, C will have a Fig. 14A build platform speed associated with it. The minimum speed will be used to move the build platform from layer n-1 to layer n. That minimum speed will be used to select a table from among Figs. 14B-14D and to select from that table the GSi grayscale value for each region, based on the region's surface area, inverse slenderness, and void ratio. As mentioned above, the grayscale values are preferably partial grayscale values that are combined with grayscale values based on the overlap of the part with a pixel defined by a DLP® mirror and/or based on to light compensation to account for varying intensities in the xy plane.

Another method, not forming part of the present invention, for manufacturing a three-dimensional object by solidifying a solidifiable material will now be illustrated with reference to Figs. 14A and 14B. As with previous methods, a photohardening inhibitor is provided to create a dead zone 41 beginning at a surface 27 of the settable material 25 which is impinged upon by the setting energy.

The procedure uses a geometric parameter called the "longest minimum path" or "LMP" of an independent continuous region. As used herein, "longest minimum path" refers to the radius of the largest circle that can fit within the independent continuous region. As the LMP of an independent continuous region increases, the rate of movement of fresh resin entering the space between the last solidified layer and the build plane 32 increases, which increases the pressure drop at the periphery of the region. last solidified layer and, therefore, the pressure drop between the photohardening inhibitor 47 and the periphery of the piece. An increase in pressure drop increases the flow rate of photoresist inhibitor 47 and can increase the size of dead zone 41 along the build axis (z).

According to the procedure, the longest minimum path (LMP) is determined for all regions i in a given object layer n. Figs. 14A and 14B show two independent continuous regions 86 and 94 with region indices 1 and 2 for a given object layer. In FIG. 14A three circles 88, 90 and 92 are shown touching the edge of the separate continuous region. 86. Any number of circles having index j ⁼ 1 to j ^max can be "drawn" (mathematically, not necessarily graphically) by creating a grid of possible center points within the independent continuous regions and adjusting the radius of circles at each center point until contact is made with the edge of the independent continuous region. The largest circle is 92, which has a radius of í ^m . Therefore, the LMP for the layer ne i =1 is rM.

In FIG. 14B shows two circles 96 and 98. Circle 96 is the largest circle that can fit within the independent continuous region 94. Therefore, its radius ^{í i} is the LMP for shell n and i = 2. The LMP for the entire layer is the maximum of the LMP values for all regions i. Thus, if the independent continuous regions 90 and 94 were the only two regions in a layer n, the LMP for the layer would be ^ím . Therefore, the maximum LMP for an independent continuous region i can be expressed as follows:

( 11) LMP ni ⁼ Max ( rn,ij)p«raj ⁼ 1 at jmax

where LMP ⁿⁱ = minimum longest path for the independent continuous region i

í ^nij = radius of the j-th circle within the i-th independent continuous region of the n shell;

i = independent continuous region index;

j = circle index; Y

n = layer index.

The LMP for layer n ( LMP ⁿ ) can be expressed as follows:

The dead time t ^d for a given layer is a function of the LMP for the layer, that is, LMP ^n:

A series of exposure times t ^e , t ⁿ¹ , t ⁿ² ... t ^{nmax is determined} for each layer. Each exposure time corresponds to a pattern of solidification energy that can be defined, for example, by means of a bitmap and corresponding to one or more of the independent continuous regions in an object layer. The first layer exposure time t ^e will be determined as described above and will constitute all independent continuous regions of a layer. Each successive pattern will exclude the next independent continuous region with the lowest longest minimum path (LMP) in that layer, and the exposure time for any given pattern (bitmap) will be determined based on the smallest LMP for any of the independent continuous regions remaining after excluding the next layer in sequence. Therefore, with reference to Figs. 14A and 14B, if regions 86 ( i=1) and 94 ( i=2) are the only two independent continuous regions in layer n, the first exposure will include both regions 86 and 94 for an exposure time t ^e (given as described above). The second exposure will include only region 86 and will occur during an exposure time t ⁿⁱ . Exposure times can be determined experimentally to create a continuous or discrete function that relates exposure times to the smallest remaining LMP longest minimum path in the next pattern (bitmap).

EXAMPLE 5

The same material, inhibitor chamber 46 pressure, and DLP brightness are used as in Example 2. Oxygen is the inhibitor. The maximum LMP values for a layer and the corresponding values of the dead time t ^d and the full layer exposure time t ^e are shown in Table 1:

TABLE 1

Using Table 1, if a particular independent continuous region is exposed with smaller regions, the exposure time for the larger region (and those larger than it) is determined by taking the value in the right column and subtracting the Previous exposure times determined for regions with smaller LMP values. For example, a larger region having an LMP greater than 15.5mm will be exposed for a cumulative time of 7.5 seconds. However, when that larger region is exposed, the sum of the previous exposure times generated from the smaller LMP regions will be subtracted from 7.5 seconds, so that the cumulative exposure time for the LMP region larger is 7.5 seconds.

For example, layer n-1 includes three independent continuous regions A ¹ , A ² and A ³ . A ¹ has an LMP between 0 and 2.5 mm. A ² has a LMP between 4.5 and 7.5 mm. A ³ has a LMP greater than 15.5 mm. Layer n is formed as follows: Build platform 26 ascends along the build axis (z) for a dead time of 7 seconds (because the maximum LMP for the entire layer is greater than 15.5 mm), during which not enough energy is projected to solidify the solidifiable material. Since the smallest region has an LMP between 0 and 2.5 mm, solidification energy is projected for each independent continuous region (A ¹ -A ³ ) during an exposure time of 6 seconds (t ^e ). Solidification energy is then projected for the independent continuous regions A ¹ and A ² for an exposure time of 1 second ( tni). The 1-second exposure time is obtained by taking the cumulative exposure time for the shorter of ^A1 and ^A2 (7 seconds for ^A1 ) and subtracting all previous exposure times (6 seconds). Solidification energy is projected for area A ³ for an exposure time of 0.5 seconds. This exposure time is obtained by taking the cumulative exposure time for A ³ (7.5 seconds) and subtracting the sum of the previous two exposure times (6 seconds 1 second= 7 seconds) to 7.5 seconds, giving 0.5 seconds.

The present invention has been described with reference to certain exemplary embodiments thereof. However, it will be readily apparent to those skilled in the art that the invention may be embodied in specific forms other than the exemplary embodiments described above. The exemplary embodiments are illustrative only and should not be considered restrictive in any way. The scope of the invention is defined by the appended claims and their equivalents, rather than the preceding description.

Claims (15)

1. An apparatus for manufacturing a three-dimensional object (24), comprising: a photoresist container (28) having an inhibitor-permeable surface that is permeable to a photoresist inhibitor (47); a build platform (26) movable along a build axis relative to the photoresist container (28); a source of freezing energy operable to project images of freezing energy through the inhibitor-permeable surface; at least one controller having a processor and computer-readable memory having instructions stored therein, wherein when executed by the processor, the instructions cause the controller to carry out a procedure, the procedure being characterized in that understands: alternating between sets of continuous solidification energy image exposure periods and sets of discontinuous solidification energy image exposure periods, wherein during each set of continuous solidification energy image exposure periods, the energy images Corresponding to cross-sections of the three-dimensional object (24) are continuously projected onto a surface of the photoresist material (25) as the build platform (26) moves continuously a distance along an axis corresponding to a selected number of object layers, and during each set of discontinuous solidification energy image exposure periods, the build platform 26 moves discontinuously along the build axis, and the solidification energy images corresponding to cross sections of the three-dimensional object Final (24) are discontinuously projected onto the surface of the photoresist material (25) only when the build platform (26) is stationary along the build axis to solidify the selected number of object layers. 2. An apparatus according to claim 1, the method further comprising admitting a photoresist inhibitor (47) through the surface of the photoresist material (25). 3. An apparatus according to claim 1 or 2, wherein the largest continuous cross-sectional area of the three-dimensional object (24) is at least about 1.5 cm ² . 4. An apparatus according to claim 3, wherein the selected number of object layers is not greater than ten. 5. An apparatus according to claim 4, wherein the largest continuous cross-sectional area of the three-dimensional object (24) is at least about 2.5 cm ² . 6. An apparatus according to claim 5, wherein the selected number of object layers is not more than five. An apparatus according to any one of claims 1 to 6, wherein during each of the continuous solidification energy period sets, a velocity of the build platform (26) along the build axis in a direction away from the surface of the photoresist material (25) varies according to the following relationship: dz/dt = (1 /t ^e ) (Az) where Az = selected layer thickness during the solidification energy period (microns, p); dz/dt = build platform velocity along the build axis (p/s); t ^e = exposure time per image (s). 8. An apparatus according to claim 7, wherein the speed of the build platform along the build axis varies between about 2 mm/s and about 6 mm/s. An apparatus according to any of claims 1 to 8, wherein after each exposure during each batch solidification energy exposure period, the build platform (26) is moved away from the surface by a first greater distance than the selected layer thickness, and then moves toward the surface a second distance equal to the first distance minus the selected layer thickness. 10. An apparatus according to claim 9, wherein the first distance is two to ten times the selected layer thickness. 11. An apparatus according to any of claims 1 to 10, wherein the step of continuously projecting images of solidification energy corresponding to cross-sections of the three-dimensional object on a surface of the photoresist material (25) is carried out by projecting two-dimensional images onto the surface of the photoresist material (25). An apparatus according to any of claims 1 to 11, the apparatus further comprising a construction plane (32) defined by a dead zone (41), which is a region into which solidification energy penetrates but in which the photocurable material (25) does not harden. 13. An apparatus according to any of claims 1 to 12, wherein the container (28) includes a transparent bottom (36) comprising a rigid or semi-rigid material. 14. An apparatus according to claim 13, wherein the semi-rigid material is glass or plastic. 15. An apparatus according to claims 1 to 14, wherein a pattern generator (37) provides the image to the photocurable material (25) to selectively solidify it.